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Calling via Voice over IP using apps such as Skype, Viber and WhatsApp is common nowadays, but in traffic records, these calls are included with all the other data transfers. Voice over IP calls may lead to different exposure levels for people than other data usage since the position in which the phone is held could be different than for other data usage such as web surfing. Telecom ParisTech has modified the XMobiSense app, previously used in several epidemiological settings, to record details of data transfers. The app updates are crucial in order to adapt to the stunningly rapid evolution of the Android operating system.

Antenna impedance measurements are usually performed with a coaxial cable connected to the RF input port. For miniature or very integrated antennae, the presence of a coaxial cable can alter drastically the impedance and radiation behaviors. In this paper a new broadband measurement method based on RF/optical transceivers device which avoid the coaxial cable disturbance is presented. A validation based on an arbitrary load and a canonical antenna measurement is proposed. An implemented use case is presented for a TETRA Pager.

The study presented in this paper deals with the liquid–gas phase change by pressure decline of supersaturated CO2 solutions in 2D porous media. The growth of the gas phase is studied experimentally and numerically as a function of supersaturation, wettability and gravity. Experiments are performed on a transparent etched network (micromodel) and simulations with a specific numerical automaton. In the experiments, the nucleation process, i.e. the occurrence of the gas bubbles, as well as the growth of these bubbles are visualised and analysed by means of a micro video camera and an image processing apparatus. The observations confirm the heterogeneous nature of nucleation and the disordered growth pattern of the gas phase. The analysis of the growth rate of a single gas cluster shows that this phenomenon is different from the compact growth of an isolated single bubble in the bulk. As previously predicted, the bubble growth by mass transfer and volume expansion in porous media is characterised by a pattern of the invasion percolation type under normal laboratory conditions. Numerical simulations of the growth pattern and the growth rate of a single gas cluster are performed with a numerical automaton. Based on a pore network modelling technique and a set of hypotheses derived from the observations, this automaton is first validated by comparing the numerical results with the experiments. Then, the automaton is used to conduct a sensitivity study. In particular, the influences of the Jakob number, pressure decline rate, Bond number, wettability and characteristics of the microstructure are investigated.

In many hydrological applications, the modelling of water infiltration in soil is based either on Richards' equation or on the empirical concept of field-capacity utilized by capacity-type models. These two approaches feature different integration scales, and are often presented as antagonistic, with the former being physically correct and the latter a practical surrogate, however flawed by uncertain parameters. Here, we conducted a theoretical appraisal of a generic capacity model by comparing its predictions of water content in a macroscopic layer subjected to a constant surface infiltration flux with a length-averaged analytical solution of Richards' equation. We show that the choices of the time and spatial scales for the empirical model are not arbitrary, and discuss the cases in which they lead to an agreement with the mechanistic description, for a range of initial and boundary conditions, and for three soil types (sandy, loamy, and clayey). The concept of field-capacity hardly applies for the sandy soil because of its high hydraulic conductivity, but yields good results for finer textured soils. Provided that layer thickness exceeds 15 cm, capacity-type predictions had a 50 probability of being within 20 of mechanistic solutions, without requiring the hydrodynamic characterisation of the soil.

Two-phase (air-water) flow experiments were conducted in horizontal artificial fractures. The fractures were between glass plates that were either smooth or artificially roughened by gluing a layer of glass beads to them. One smooth fracture with an aperture of 1 mm and three rough fractures, one with the two surfaces in contact and two without contact, were studied. For both types of fractures, the flow structures are similar to those observed in two-phase flow in a pipe, with structures (bubbles, fingering bubbles, films, and drops) depending on the gas and liquid flow rates. The pressure gradients measured for different liquid and gas velocities were interpreted by three models. First, using Darcy's law leads to relative permeability curves similar to conventional ones for porous media. However, these curves depend not only on saturation but also on flow rates. This effect is caused by inertial forces which are not included in this approach. Second, the standard approach for two-phase flow in pipes (Lockhart and Martinelli's equation) agrees with experimental results, at least for small pressure gradients. Finally, the best fit was obtained by treating the two phases as one homogeneous phase. All the properties are averaged, and the pressure drop is deduced from an empirical correlation between the two-phase Reynolds number and the friction factor.

International audience; This paper investigates the impact of realistic antennas on joint anchor-less localization and indoor characterization based on Impulse Radio (IR) Ultra Wideband (UWB) communications. In this frame, the Maximum Averaged Likelihood (MAL) algorithm and its extended version are considered, both relying on a tree approach consisting in two stages. The first part of the process, which is common to both algorithms, exploits the cross-correlation between received and locally predicted paths. The second stage calculates the averaged likelihood of measured path parameters obtained in the previous step, but different measurements are used for MAL and extended MAL (eMAL). In the first algorithm, only the Angle of Incidence (AoI) and the Time of Arrival (ToA) are considered, whereas the eMAL tree algorithm also accounts for two couples of Angles of Departure (AoDs) and Angles of Arrival (AoAs). The estimation errors of both nodes coordinates and room dimension obtained with the two algorithms are compared for three realistic UWB antennas. Finally, the remaining algorithm-independent ambiguities (i.e. resulting from scenario and geometry) are discussed.

International audience; This paper investigates hybrid fiber-radio networks for in-building distribution of ultrawideband (UWB) signals, in order to extend UWB radio coverage area. An original multipoint to multipoint UWB-over-fiber system, proposed in the frame of BILBAO project, is presented and discussed. System link gain and noise figure are evaluated through theoretical analysis. A simulation model is used to study the impact of E/O transceivers nonlinearity on UWB signals. Experimental results show good agreement with simulation results. A high data rate file transfer, with UWB radio propagation and transmission over 100 m of multimode fiber, has been also successfully demonstrated.

International audience; We show for the first time the feasibility of a multipoint to multipoint architecture for the distribution of ultra wide band radio signals over multimode fibre with low cost components. In a few years home networks will have to work at speeds of 1 Gbit/s following the deployment of fibre to the home and to satisfy the explosion of broadband services [1]. Preferably, such a network should have a wireless connectivity. Ultra Wide Band (UWB) radio is able to provide high bit-rates, but with coverage limited to a few metres [2-3], thus Radio over Fibre (RoF) distributed antenna systems become of interest to extend the UWB coverage. Previous papers have addressed the transmission of pulsed and OFDM based UWB on optical channels only [4-6]. Two recent works have shown the feasibility of UWB over multimode and single-mode fibre [7-8] respectively, but only in the case of a point to point (Pt2Pt) architecture. Here, we present the results of the French BILBAO project that investigates architectures and low cost solutions for a home UWB based network on multimode fibre (MMF). We focus on OFDM UWB in the 3-5GHz band.

In this paper, we compare various UWB antennas according to their impact on performances of a coherent Rake receiver system. As such receiver may suffer from ISI effect, the aim of this study is to evaluate two typical UWB antennas used in classical indoor communication scenario regarding the system bit error rate versus signal SNR. In order to assume the same channel for the two couples of considered antennas, a deterministic channel model is used for simulation. This channel is first presented. The whole UWB system simulation scheme considered for the study is then detailed. The obtained results show the performances of a UWB coherent Rake receiver system are less degraded by dipole-like antennas than monopole-like ones according to ISI effects. (6 pages)

The co-design between an antenna and a low noise amplifier (LNA) is here addressed over an ultra wide frequency bandwidth: 3.1-5.1 GHz. The key idea of co-design is to relax the 50 Ω impedance matching constraint on both LNA and antenna thanks to joint conception in order to improve performances for a given power budget. On LNA side, the co-design benefits from removing the major part of the costly integrated passive elements serving as a matching circuit. The co-designed LNA benefits from a size, cost and noise figure reduction. The antenna input impedance has no more to fit constant and real impedance on the whole bandwidth. In the present case, this point is used to reduce dimensions. To quantify performance enhancement the followed strategy consists in comparing a classical 50 Ω and a co-designed active antenna design approach, with the same LNA architecture, the same power consumption and the same antenna kind. (5 pages)

A 1 V wireless SoC embedding an RF transceiver, a sensor interface, a 6.4 MHz RISC micro-controller with an 8k instruction SRAM and a power management unit is reported. The radio supports 25 kb/s FSK and 2 kb/s OOK modulations in the 433/868 MHz bands. In the 433 MHz band, the receiver draws 2.1 mA while providing a sensitivity of -108 dBm and the transmitter draws 27.6 mA for an output power of 10.5 dBm.

Spatial diversity is regarded as a possible mean to relax the stringent constraints imposed by regulations on link budget for ultra wide band (UWB) communications. After general considerations on the pertinence of diversity for UWB signals, it is shown here by simulations on a test array, that electromagnetic coupling between sensors should be negligible, allowing one to use diversity for improved energy capture. In addition, the computation of fading signal probability distributions shows a good hope of fading mitigation by spatial diversity, in the case of a frequency mode UWB modulation.

Nucleation and growth of bubbles in porous media are important problems encountered in processes such as pressure depletion and boiling. After a recap of the basic principles of nucleation and bubble growth in the bulk, we discuss some of the results obtained during the last ten years within the framework of percolation and pore network models. In particular, results of experiments of liquid-to-gas phase change by pressure decline of supersaturated CO2 solutions in 2D transparent etched networks are reported in order to understand the phenomena in porous media. The observations confirm the heterogeneous nature of nucleation, i.e., the decisive role of the capillary roughness of the pore walls. Contrary to the bulk or Hele–Shaw cells, gas clusters have irregular and ramified shapes typical of invasion percolation patterns. As a result, the growth rate of a single gas cluster is different than the growth rate of an isolated single bubble in the bulk. Numerical simulations of the growth pattern and of the growth rate of a single gas cluster are performed with a numerical automaton. Based on a pore network modelling technique and on a set of hypotheses derived from the observations, this automaton is first validated by comparing the numerical results with the experimental data. Then the automaton is used to explore the influences of the Jakob number, pressure decline rate, Bond number, and wettability. In a last part, the closure of the macroscopic mass balance equations is discussed.

Physical Mechanisms for Bubble Growth during Solution Gas Drive. Abstract A series of experiments were performed in transparent micromodels to understand the mechanism of nucleation by pressure decline in a CO2-water solution. All our observations can be interpreted by a process that consists in the following succession of steps:pre-existence of stabilized microbubbles (order of magnitude of one micron),growth of the microbubbles in a very large number of sites and trapping by capillary forces,activation of some of these sites when pressure drawdown balances capillary trapping,growth of these bubbles by gas diffusion to a size allowing observation (around 30 microns). The above process is similar to the one found in literature explaining boiling on heated surfaces. Introduction In petroleum engineering, there is a need for modelling gas production in reservoirs when pressure decreases below the bubble point. Modelling of gas production requires an accurate description of the three physical mechanisms involved in the process:the rate of appearance of gas bubbles,the growth of bubbles inside the pores,the formation of a continuous gas phase which will invade the medium. The physical mechanisms governing the second and third steps are quite well understood. For instance, bubble growth inside pores is described by molecular diffusion with some correction factors to account for the presence of the porous medium (Li and Yortsos). However, the understanding of the first step, bubble formation inside a porous medium, is quite poor. The few existing models found in petroleum literature are contradictory. The classical model is derived from "homogeneous nucleation" (Wilt, Li and Yortsos). A recent paper by Firoozabadi and Kashiev, propose a completely different approach based on instantaneous nucleation. In order to improve the understanding of bubble appearance, we performed visualisations and measurements in transparent micromodels. The conclusion of our work is that nucleation is instantaneous, but not so simple than the model proposed by Firoozabadi and Kashiev. In fact, there is an additional step of trapping due to capillary force that explains the observed threshold and the progressive appearance of the bubbles. Heterogeneous nucleation. We will first recall the principle of "homogeneous" nucleation, when the liquid is pure, without any solid or liquid interface. When pressure is decreased under the bubble point, a transient gas "nucleus" appears by thermal fluctuations. This nucleus will grow in order to form a bubble only if its radius r is larger than a critical value. Otherwise, the nucleus will collapse under capillary pressure proportional to l/r (Laplace's law). The appearance of bubbles is therefore a random process such as photon emission, characterized by a rate of nucleation J (number of bubble per unit time and unit volume of liquid). J is an exponential function of the supersaturation P=P(equilibrium)-P (1) where N is the number of molecules per unit volume, m the mass of a molecule, kT is thermal energy, interfacial tension and B a parameter close to 2/3. It is now well established that homogeneous nucleation requires a very high supersaturation ratio P/P. Wilt gave the example of 1100 to 1700 for CO2 solutions near room conditions. Consequently, homogeneous nucleation cannot occur during pressure decline in porous media (Li and Yortsos). Instead, gas formation with low supersaturation rates can only be explained by "heterogeneous" nucleation. In heterogeneous nucleation, the nucleus is formed on a solid interface. The nucleus is stabilized by the combined effect of surface roughness and wettability (Wilt, Li and Yortsos). For instance, it is simple to show that in a site of conical geometry with an angle, the interface between liquid and gas is flat when the contact angle is equal to /2- /2. There is no curvature of the interface and therefore there is no capillary pressure to collapse the nucleus. Consequently, hydrophobic sites reduce the energy involved for nucleus formation and can explain gas nucleation at low supersaturation rate. P. 805^

Plusieurs difficultes fondamentales concernant le comportement des antennes ultra large bande operant en regime impulsionnel et rendant leur conception delicate sont evoquees. Cela concerne la deformation temporelle du signal emis, l’adaptation d’impedance, la moins facile separabilite antenne-canal-antenne, ou encore l’impossible existence d’antennes a la fois petites et a tres large bande. Des indicateurs de performance sont proposes pour aider a l’analyse du comportement et a la caracterisation des antennes, ainsi que 2 definitions d’antennes « ideales » utiles en tant que reference. On compare le comportement temporel de plusieurs antennes ULB typiques reposant sur des principes differents, montrant des imperfections dans la reponse impulsionnelle en relation avec la nature de ces antennes.

Resume Les phenomenes couples de transferts de chaleur et de masse qui se developpent dans un milieu poreux non sature homogene et isotrope soumis a de faibles gradients de temperature, lorsque la pression de la phase gazeuse est uniforme et constante et l'influence de la gravite negligeable, ont ete analyses a partir d'une etude experimentale et d'une simulation numerique des regimes transitoires hydrique et thermique. Les coefficients intervenant dans le systeme d'equations ayant fait l'objet de determinations independantes de la procedure de simulation physique, la comparaison entre resultats experimentaux et numeriques a permis d'apprecier la validite du modele de description mathematique.

Resume Le concept de coefficient de transfert a ete utilise pour la modelisation en regime permanent de mouvements thermoconvectifs en milieu poreux. Les resultats numeriques obtenus, largement representatifs de la realite experimentale, mettent en evidence l'influence, sur le transfert de chaleur moyen, du degre de division du milieu et des caracteristiques thermiques des phases le constituant.

Resume La convection naturelle d'origine thermique qui se developpe dans une cavite poreuse de section droite circulaire d'axe vertical limitee horizontalement par deux surfaces isothermes impermeables et lateralement par un materiau impermeable de conductivite thermique donnee, est etudiee par voie theorique. Les resultats presentes concernent principalement les criteres de stabilite et le transfert de chaleur moyen. Ils sont explicites en fonction du rapport de forme (extension verticale sur diametre de la cavite) et du rapport des conductivites thermiques milieu poreux-paroi.

Unavoidable level and flow measurement errors, the very definite uncertainty as to how loss to head varies with depth of water, and variations in the coefficient of frictional resistance all combine to limit the possibilities of reproducing free-surface flows. It seems to be interest, therefore, to examine the similitude conditions whereby given prototype and model flows could be made to correspond to within a degree of approximation not exceeding the degree of uncertainty attached to the evaluation of the relevant characteristic parameters. The basic idea is thus to define similitude conditions enabling an operating point on the prototype to strictly correspond with on the model, and which is approximately satisfied near these "reference operating points". This is by no means a new assumption, as it has already been used implicitly in backwater curve calculation methods (e.g. Bakhmeteff) or simplified procedures for the investigation of transient regimes. The authors have considered two possible approaches, one of which makes use of the equivalence of flows in prismatic and very broad channels, and the other being based on profile similitary. In the case of steady flow conditions, the authors have attempted to base the definition of similitude criteria on the intuitive idea of conserving both Froude number and the slope J/I of the hydraulic gradient J with respect to the longitudinal canal slope I in the vicinity of two homologous "reference points". By using non-dimensional quantities, non-dimensional groups G (h) and M (h) are obtained; these are considered in the definition of the similitude parameters, being similar, to the non-dimensional critical flow rate and characteristic slope defined by Lazard and Silber. The local conservation of Froude number and the J/I ratio is not sufficient to ensure approximate similitude for transient flow conditions, however, for which a third condition "S/BM = a constant" has to be added. The conjunction of these three assumptions is only possible where the profiles can be transformed by similarity. For the general case, the validity has been examined of a similitude condition based on the constancy of J/I and S/BM. These approximations are comparable to those considered for the basic assumptions made for graphical constructions using the depth of water and discharge functions H and Q; they nearly always give satisfactory results. All things considered, however, the experimental approach still remains the most reliable basis of assessment for the validity of this approximate similitude. The first tests have shown that, allowing for unavoidable measurement error, agreement between flows connected by these similitude rules is satisfactory, especially for structures of moderate length. The "hyperdistorted" similitude discussed above is a transformation which makes flows correspond rather than structures. It only hold good within a limited range of depth variations about a reference depth. Its three possible types of application are the following: 1. Investigation of a flow similar to the basic prototype flow on a scale model differing in profile from the prototype. A laboratory Hume with its sides set at a certain slope can be used to study transient How conditions for a different structural profile. 2. Attempted classification of transient flows into groups. Geometrical similitude__and even more so longitudinally distorted similitude__enable a whole "family" of flows to he associated with flows observed on the model or the prototype. 3. Study of equivalent tangent flows in very broad flames. The "hyperdistorted" similitude notion also facilitates use of the equivalence between basic and tangent flows in very broad flumes. Flows of this sort are of very valuable assistance for graphical constructions.

A rapid and sensitive liquid chromatographic (LC) method for determination of trace amounts of chloramphenicol (CP) in animal tissues has been developed. Chloramphenicol identity is confirmed by gas chromatography-mass spectrometry (GC-MS). CP can be routinely quantitated by LC at 10 ppb with 75% recovery, and GC-MS selected ion monitoring permits complete identification at concentrations as low as 5 ppb. Residues were determined in chicken tissues after intramuscular injection of CP. Depletion was rapid with no residues detected in muscle after 8 h, while 15-30 ppb CP was still determined and identified in the liver.

Heat and mass tranfer in the presence of phase change in porous media play a very important role in the production of hydrothermal reservoirs. After a literature review of this field the equations describing heat and mass transfer are presented and used to derive dimensionless quantities governing the phenomena. Recent numerical modelling of these equations are also analysed and discussed.

Previous experiments on natural convection in a differentially heated porous layer with large lateral dimensions gave evidence for different configurations of flow. Depending on the values of the Rayleigh number, the inclination and the longitudinal extension of the layer, the three main structures observed correspond to a two-dimensional unicellular flow, polyhedral convective cells and longitudinal coils. In this paper there is a definition of the conditions necessary for these types of flow to exist using a linear stability theory and it is shown that the experimentally observed structures can be theoretically predicted by a three-dimensional numerical model based upon Galerkin's spectral method. Finally, the results of this model are used to show the influence of initial conditions on the setting up of the stationary flow.